The present invention relates generally to methods and apparatus utilized in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides a compact electrohydraulic actuation system for downhole tools used in subterranean wells.
It would be desirable to be able to operate selected ones of multiple hydraulically actuated well tools installed in a well. However, it is uneconomical and practically unfeasible to run separate hydraulic control lines from the surface to each one of numerous well tool assemblies. Instead, the number of control lines extending relatively long distances should be minimized as much as possible. Additionally, it would be desirable to effect the operation of multiple hydraulically actuated well tools with a relatively low power consumption control system.
Therefore, it would be highly advantageous to provide a hydraulically-based control system and associated control methods which reduce the number of control lines extending relatively long distances between multiple hydraulically actuated well tools and the surface. The control system would preferably permit individual ones of the well tools to be selected for actuation as desired, and the selection of well tools should be convenient and reliable.
In carrying out the principles of the present invention, in accordance with an embodiment thereof, a compact hydraulic actuator and associated methods are provided which solve the above problem in the art.
According to one aspect of the invention, a downhole well tool assembly, representatively a flow control device in the form of a variable inlet choke device, is controlled using a fluid power source connected thereto and including a first source of pressurized fluid operable to power the downhole well tool assembly via a first fluid circuit portion connectable to the downhole well tool assembly, and a second source of pressurized fluid having a second fluid circuit portion interposed in the first fluid circuit portion, the second source of pressurized fluid being operable to selectively alter the routing of pressurized fluid to the downhole well tool assembly. The fluid power source is preferably disposed entirely downhole, and is electrically operable.
In an illustrated embodiment of the actuator, the first source of pressurized fluid includes a reciprocating hydraulic primary pump which is coupled to the well tool assembly by the first circuit portion, and has a reversible electric drive motor. Check valves interposed in the first circuit portion the primary pump a double pumping action. The second source of pressurized fluid includes a reciprocating hydraulic switching pump used to control fluid pressure operable pilot check valves in the second fluid circuit portion and in a manner selectively reversing the fluid supply and return flow directions to the controlled well tool assembly via the first fluid circuit portion.
In the illustrated embodiment of the actuator, the actuator construction includes a body having first and second bores extending therethrough, the first and second bores respectively having radially enlarged first and second cylinder portions with opposite ends. First and second rods are reciprocably disposed in the first and second bores and have radially enlarged piston portions slidably received in the first and second cylinder portions and dividing each of them into opposing first and second hydraulic chambers that may be coupled to fluid circuitry. First and second drive portions extend outwardly from the body and have reversible electric motors respectively coupled to the first and second rods, to reciprocate them in the first and second body bores, via gearing and ball screw structures.
According to another aspect of the invention, a pilot check valve is carried in the first bore and is connectable to the first fluid circuit portion, the pilot check valve being selectively engageable ay an end portion of the first rod to disable the fluid flow blocking function of the pilot check valve.
In accordance with another aspect of the invention, a first accumulator is communicated with the first fluid circuit portion, is chargeable by the first source of fluid pressure, and is selectively communicatable with the controlled well tool assembly to rapidly open or close a control drive portion thereof. A second, smaller accumulator is preferably interconnected between the first accumulator and the first fluid circuit portion, and functions to maintain a minimum fluid pressure in the first fluid circuit portion.
In accordance with a further aspect of the present invention, a well completion is provided in the wellbore of which are provided a spaced series of downhole well tool assemblies which are representatively flow control devices in the form of variable fluid chokes. Each flow control device is operatively connected to one of the downhole hydraulic actuators, and, according to a method of the present invention, a control system is used to sense the magnitudes of predetermined operational parameters of the chokes and responsively control the operation of their associated first and second sources of pressurized fluid in a manner maintaining the magnitudes of the sensed operational parameters at predetermined levels.
Representatively, the sensed operational parameters are fluid pressure drops across the variable inlet opening areas of the chokes. In various representative embodiments of this control method, the control system is operative to maintain predetermined minimum fluid pressure drops across the inlet opening area, representatively by maintaining predetermined minimum positive exterior-to-interior fluid pressure drops across the inlet opening areas, or may be operative to maintain substantially equal fluid pressure drops across all of the variable inlet opening areas.